made wget as Linux default and curl as OS X default for pyqt5_check.py, since OS X doesn't have wget installed be default and Linux may not have curl by default.  Feedback on this welcome
made wget as Linux default and curl as OS X default for pyqt5_check.py, since OS X doesn't have wget installed be default and Linux may not have curl by default.  Feedback on this welcome

scholer/cadnano2.5